Circulation of digestion liquor in sulfite pulp boiling



Jan. 11, 1955 c. J. LOCKMAN 2,699,390

CIRCULATION OF DIGESTION LIQUOR IN SULFITE PULP BOILING Filed Feb. 17, 1954 j. F/y. Z.

i rzza 13b 13 j b mmg 1 INVENTOR. CARL JOHAN LOG/(MAN United States Patent CIRCULATION OF DIGESTION LIQUOR IN SULFITE PULP BOILING Carl Johan Lockman, Stockholm, Sweden, assiguor to Aktiebolaget Rosenblads Patenter, Stockholm, Sweden, a joint-stock company of Sweden Application February 17, 1954, Serial No. 410,925

Claims priority, application Sweden February 19, 1953 4 Claims. (Cl. 92-7) The present invention relates to circulation boiling of sulphite pulp, and more particularly to heating of the digestion liquor in a heat-exchanger or so-called calorisator.

In carrying out such heating it has been observed that the heating surface in the digestion liquor passage of the calorisator is liable to get incrusted towards its outlet and for a distance which is less than one half, and frequently not greater than a fourth, of the total length of said passage, whilst the remainder of the heating surface will remain unobstructed by such incrustations or scales. The incrustations or scales mainly consist of plaster (calfium sulphate) which has been dissolved in the digestion iquor.

This phenomenon may be explained in the following way forming the basis of the present invention:

Since plaster precipitates in the downstream portion of the calorisator the digestion liquor must enter the boiler or digester saturated with plaster, at the temperature imparted thereto in the calorisator, and, in addition, it will contain plaster in a suspended state. In the digester the plaster particles thus suspended will precipitate onto the pulp fibres which act as a filter, and in the course of its passage through the digester, the liquor will heat the contents of the digester and will thus have its temperature reduced. Since, as is well known, the capability of the liquor to dissolve plaster is increased with decreasing temperature, within the ranges of temperature considered in this case, the liquor will, therefore, on leaving the digester and entering the calorisator have a plaster content lower than the saturation value. Therefore, no plaster precipitation onto the heating surface of the calorisator will occur until, during its recirculation through the calorisator, the liquor has again become heated in excess of the saturation temperature, and this will not take place until the liquor has proceeded along the major portion of the heating surface. Before this occurrence the digestion liquor is even capable of dissolving plaster.

The main object of the present invention is to utilize the condition just explained.

A further object of the invention is to cause the digestion liquor to flow through the calorisator periodically and alternately in opposite directions so that in each period of through-flow the digestion liquor flowing from the boiler will be introduced onto that portion of the heating surface of the calorisator from which the digestion liquor was discharged from the calorisator to the boiler during the next preceding period. In this way, during each period of through-flow, non-saturated digestion liquor will dissolve plaster incrustations formed during the next preceding period.

Another object of the invention is to adjust the interval between the flow reversals to the actual rate of formation of the incrustations so as to limit the maximum thickness of the incrustations formed in each period to a value which will not materially affect the efficiency of the heat transfer in the calorisator.

The invention will now be more closely explained in conjunction with the accompanying drawing illustrating, by way of example and in a purely diagrammatic manner, three specific embodiments and in which:

Figures 1 and 2 illustrate the digester and calorisator and associated ducting according to one embodiment of the invention and in two different operative conditions, respectively, the digester being omitted from Figure 2 for simplicity of illustration.

2,699,390 Patented Jan. 11, 1955 Figures 3 and 4, in a manner similar to Figures 1 and 2, illustrate a second embodiment of the apparatus for carrying the invention into effect, and

Figs. 5 and 6 illustrate a further embodiment of apparatus for carrying the invention into effect and do so in a dmanner generally similar to the showings of Figs. 1 an 2.

Referring now to Figures 1 and 2 of the drawing, 1 denotes a boiler or digester and 2 a calorisator which has through-flow passage for the digestion liquor in the form of a set of tubes 3. The tube set can be put in communication alternately at either of its two ends with, on one hand, an outlet duct 4 for digestion liquor coming from the digester through a two-way valve 5, conduits 6a and 6b and pipe connections 7a and 7b, and, on the other hand, an inlet duct 8 for digestion liquor to the digester through a two-way valve 9, conduits 10a and 10b and pipe connections 11a and 11b. The outlet duct 4 has a pump 12 inserted therein. Steam for heating purposes is supplied to the space around the tubes within the calorisator through a conduit 13, and the condensate from the heating steam is drained from said space through a conduit 14 and a drain valve 15.

In the arrangement described, the digestion liquor will be passed from the digester 1 through the pump 12, conduit 4, valve 5, conduit 6a and pipe connection 7a, then through the set of tubes 3 in an upward flow while being heated from the heating steam; and thence through the pipe connection 11a, conduit 10a, valve 9 and back to the digester through the inlet duct 8.

During this circulation incrustations will be formed in the top end portion of the set of tubes. Before these incrustations have had sufiicient time to build up to a thickness which would be detrimental to the operation, the valves 5 and 9 are shifted into the positions illustrated in Figure 2, causing the digestion liquor to be introduced into the calorisator 2 through the top inlet conduit 6b and connection 7b, and to be discharged from the same through the connection 11b and the lower conduit 10b. In this case the digestion liquor will instead be passed through the tube set of the calorisator in the downward direction, whereby liquor non-saturated with plaster will sweep and dissolve the incrustations formed in the top portion of the tube set during the preceding operating period, and at the same time new incrustations will build up in the lower portion of the tube set. The latter incrustations, in turn, will be removed during the next succeeding period in which, after resetting the valves 5 and 9 into their positions according to Figure l, the digestion liquor is caused again to flow through the tube set in the upward direction, and so on.

Figures 3 and 4 illustrate a modification of the exterior ducting in accordance with a second embodiment of the invention, in which the ducts 6a and 611, on one hand, and the valve 9 and conduits 10a and 10b, on the other hand, have been replaced by goose-neck pipe sections 6 and 10, respectively. In this case the direction of flow of the digestion liquor through the calorisator can be reversed by connecting the conduit 4 alternately with the pipe connection 7a and with the pipe connection 7b, and connecting the conduit 8 alternately with the pipe connection 11a and with the pipe connection 11b. This is effected by rotating the goose-neck pipe sections 6 and 10 from the position shown in Figure 3 into the position according to Figure 4, and vice versa.

Figures 5 and 6 illustrate a further modification of the apparatus according to the invention in which a calorisator 2a of the same kind as the calorisator 2 is mounted so as to be rotatable on trunnions 16 and 17 journalled in fixed supports. All p'pe connections of the calorisator are so disposed relative to the axis of rotation that, upon rotating the calorisator through about this axis from the position shown in Figure 5 to the position shown in Figure 6, for example, all connections having the sufiix a associated with their reference numerals will occupy the positions occupied by the connections having the suffix b before the shifting operation, and vice versa.

In the position of the calorisator shown in Figure 5 the digestion liquor enters the calorisator through the connection 11b and is discharged therefrom through the connection 11a flowing through the set of tubes in the upward direction. Heating steam is supplied through the connection 13a and the condensate is drained off through the connection 14b. The remaining pipe connections are sealed. The shifting of the operating direction through the tube set is effected by loosening the pipe connections to the calorisator and removing the sealing members, after which the calorisator is rotated through 180 into the new position according to Figure 6 in which the conduit 4 is connected at 11a, the conduit 3 at 11b, the conduit 14 at 14a and the conduit 13 at 13b, and the connections thus deliberated are sealed.

Thus it is obvious that the digestion liquor, which is still caused to flow through the tube set in the upward direction, will enter the tube set and be discharged therefrom, respectively, at the opposite ends thereof as compared to Figure 5, and to the same effect as regards the incrustation dissolving feature as according to the embodiments of Figures 1 to 4.

As compared to the arrangements of Figures 1 to 4, however, an advantage will be attained in that the direction of flow of the digestion liquor in relation to the direction of flow of the heating steam within the calorisator will be invariably the same during every period of the operating cycle. This feature may be of importance in cases where, due to the calorisator design or due to the amount of steam supplied, or both, substantial pressure and temperature drops may be created at the steam-side of the heating surface. In this case the temperature differences would be of periodically different magnitudes if the relative directions of flow of the liquor and the steam were subject to reversals.

It is understood that the invention is not restricted to the specific embodiments described in conjunction with the accompanying drawing since the same is susceptible of numerous variations and modifications without departing from the scope of the invention.

What I claim is:

1. A method in sulphite pulp boiling while circulating the digestion liquor through the digester and through an external indirect heater, comprising the steps of passing the digestion liquor over one and the same heating surface of the heater in periodically changed directions in relation to said heating surface and during each period introducing the digestion liquor from the digester to that end of said heating surface from which the digestion liquoa was withdrawn to the digester during the preceding perio 2.- Means for circulating digestion liquor in sulphite pulp boiling comprising in combination a digester having an inlet and an outlet for digestion liquor, an indirect heater having a digestion liquor space and a heating medium space separated by a heat transfer wall system, a pipe connection system between the outlet for the boiling liquor from the digester and the liquor space of the heater at both ends of the heat transfer wall system thereof, valve means in said pipe connection system,

means for operating said valve means to open passage for boiling liquor to one end of and to close such passage to the other end of the heat transfer wall system and vice versa, a second pipe connection system between the liquor space of the heater at both ends of the heat transfer wall system thereof and the liquor inlet of the digester, valve means in said second pipe connection system and means for operating said second connection system to open passage for boiling liquor from one end of and to close such passage from the other end of the heat transfer wall system and vice versa.

3. Means for circulating digestion liquor in sulphite pulp boiling comprising in combination a digester having an inlet and an outlet for boiling liquor, an indirect heater having a digestion liquor space and a heating medium space separated by a heat transfer wall system, a pipe connection system between the outlet for the digestion liquor from the digester and the liquor space of the heater, a pipe unit in said pipe connection system, means for displacing said pipe unit so as to connect said system with the liquor space of the heater alternatively to one or to the other end of the heat transfer wall system thereof, a second pipe connection system between the inlet of the liquor to the digester and the liquor space of the heater, a pipe unit in said second pipe connection system, and means for displacing the latter pipe unit so as to connect said second system with the liquor space of the heater alternatively to the one or the other end of the heat transfer wall system thereof.

4. Means for circulating digestion liquor in sulphite pulp boiling comprising in combination a digester having an inlet and an outlet for boiling liquor, an indirect heater having a digestion liquor space and a heating medium space separated by a heat transfer wall system, a pipe connection between the liquor outlet of the digester and an inlet to the digestion liquor space of the heater at one end of the heat transfer wall system thereof, a second pipe connection between the inlet for the liquor to the digester and an outlet from the digestion liquor space of the heater at the other end of the heat transfer wall system thereof, and means for rotating said heater through an angle of after disconnection of said heater from its digester connections so as to enable its former liquor space outlet to be connected to the digestion liquor outlet and its former liquor space inlet to be connected to the digester liquor outlet.

References Cited in the file of this patent UNITED STATES PATENTS 1,548,477 Morterud Aug. 4, 1925 2,217,732 Dean Oct. 15, 1940 2,414,062 Richter Jan. 7, 1947 FOREIGN PATENTS 134,588 Sweden of 1952 

1. A METHOD IN SULPHITE PULP BOILING WHILE CIRCULATING THE DIGESTION LIQUOR THROUGH THE DIGESTER AND THROUGH AN EXTERNAL INDIRECT HEATER, COMPRISING THE STEPS OF PASSING THE DIGESTION LIQUOR OVER ONE AND THE SAME HEATING SURFACE OF THE HEATER IN PERIODICALLY CHANGED DIRECTIONS IN RELATION TO SAID HEATING SURFACE AND DURING EACH PERIOD INTRODUCING THE DIGESTION LIQUOR FROM THE DIGESTER TO THAT END OF SAID HEATING SURFACE FROM WHICH THE DIGESTION LIQUOR WAS WITHDRAWN TO THE DIGESTER DURING THE PRECEDING PERIOD. 